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Estrogen induces dynamic ERa and RING1B recruitment to control gene and enhancer activities in luminal breast cancer

ABSTRACT: We have previously shown that RING1B, a core Polycomb Repressive Complex 1 subunit, is amplified in 22% of breast cancer patients. In ER+ breast cancer, RING1B functionally interacts and co-localizes with ERa at enhancers and actively transcibed genes to modulate oncogenic transcriptional programs. However, the molecular mechanisms underlying this interaction is unclear. Here we demonstrate that in ER+ breast cancer cells, prolonged estrogen (E2) administration induces fluctuations in transcriptional output and chromatin landscape. RING1B loss impairs full E2-mediated gene expression and chromatin accessibility at genomic loci where key breast cancer transcription factors bind. RING1B mediates E2-induced gene expression and chromatin architectural changes both dependently and independently of its enzymatic activity and nucleosomal binding ability. We found that RING1B is recruited to ER, FOXA1, and GRHL2 co-bound sites in a cyclic manner during E2 administration and regulates E2-induced enhancers and ER recruitment. Finally, we characterized the spacial organization pattern between ER, FOXA1, GRHL2, and RING1B on the chromatin at single-nucleotide resolution genome-wide.

ORGANISM(S): Homo sapiens

PROVIDER: GSE137579 | GEO | 2020/06/08

REPOSITORIES: GEO

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Project description:FOXA1 is a pioneer factor that is important in hormone dependent cancer cells to stabilise nuclear receptors, such as estrogen receptor (ER) to chromatin. FOXA1 binds to enhancers regions that are enriched in H3K4mono- and dimethylation (H3K4me1, H3K4me2) histone marks and evidence suggests that these marks are requisite events for FOXA1 to associate with enhancers to initate subsequent gene expression events. However, exogenous expression of FOXA1 has been shown to induce H3K4me1 and H3K4me2 signal at enhancer elements and the order of events and the functional importance of these events is not clear. We performed a FOXA1 Rapid Immunoprecipitation Mass Spectrometry of Endogenous Proteins (RIME) screen in ERα-positive MCF-7 breast cancer cells in order to identify FOXA1 interacting partners and we found histone-lysine N-methyltransferase (MLL3) as the top FOXA1 interacting protein. MLL3 is typically thought to induce H3K4me3 at promoter regions, but recent findings suggest it may contribute to H3K4me1 deposition, in line with our observation that MLL3 associates with an enhancer specific protein. We performed MLL3 ChIP-seq in breast cancer cells and unexpectedly found that MLL3 binds mostly at non-promoter regions enhancers, in contrast to the prevailing hypothesis. MLL3 was shown to occupy regions marked by FOXA1 occupancy and as expected, H3K4me1 and H3K4me2. MLL3 binding was dependent on FOXA1, indicating that FOXA1 recruits MLL3 to chromatin. Motif analysis and subsequent genomic mapping revealed a role for Grainy head like protein-2 (GRHL2) which was shown to co-occupy regions of the chromatin with MLL3. Regions occupied by all three factors, namely FOXA1, MLL3 and GRHL2, were most enriched in H3K4me1. MLL3 silencing decreased H3K4me1 at enhancer elements, but had no appreciable impact on H3K4me3 at enhancer elements. We identify a complex relationship between FOXA1, MLL3 and H3K4me1 at enhancers in breast cancer and propose a mechanism whereby the pioneer factor FOXA1 can interact with a chromatin modifier MLL3, recruiting it to chromatin to facilitate the deposition of H3K4me1 histone marks, subsequently demarcating active enhancer elements.

Project description:The interplay between mitogenic and proinflammatory signaling pathways play key roles in determining the phenotypes and clinical outcomes of breast cancers. We have used global nuclear run-on coupled with deep sequencing to characterize the immediate transcriptional responses of MCF-7 breast cancer cells treated with estradiol, TNF?, or both. In addition, we have integrated these data with chromatin immunoprecipitation coupled with deep sequencing for estrogen receptor alpha (ER?), the pioneer factor FoxA1 and the p65 subunit of the NF-?B transcription factor. Our results indicate extensive transcriptional interplay between these two signaling pathways, which is observed for a number of classical mitogenic and proinflammatory protein-coding genes. In addition, GRO-seq has allowed us to capture the transcriptional crosstalk at the genomic locations encoding for long non-coding RNAs, a poorly characterized class of RNAs which have been shown to play important roles in cancer outcomes. The synergistic and antagonistic interplay between estrogen and TNF? signaling at the gene level is also evident in the patterns of ER? and NF-?B binding, which relocalize to new binding sites that are not occupied by either treatment alone. Interestingly, the chromatin accessibility of classical ER? binding sites is predetermined prior to estrogen treatment, whereas ER? binding sites gained upon co-treatment with TNF? require NF-?B and FoxA1 to promote chromatin accessibility de novo. Our data suggest that TNF? signaling recruits FoxA1 and NF-?B to latent ER? enhancer locations and directly impact ER? enhancer accessibility. Binding of ER? to latent enhancers upon co-treatment, results in increased enhancer transcription, target gene expression and altered cellular response. This provides a mechanistic framework for understanding the molecular basis for integration of mitogenic and proinflammatory signaling in breast cancer. Using GRO-seq and ChIP-seq (ER, FoxA1 and p65) to assay the molecular crosstalk of MCF-7 cells treated with E2, TNFa or both E2+TNFa.

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Estrogen induces dynamic ERa and RING1B recruitment to control gene and enhancer activities in luminal breast cancer

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